The goal of this research is to describe and then explain changes that have occurred in teenage premarital sexual and contraceptive behavior between the early and the late 1980s in the United States. Given the increase in premarital sexual activity in the teenage years, and the negative consequences attributable to teenage pregnancy, concern over adolescent sexual and contraceptive behavior spread nationwide during the 1970s. In the 1980s, concern shifted to also encompass the rise of new and often incurable STDs. Our research examines whether the changing social environment, and an accompanying emphasis on prophylaxis, are reflected in the contraceptive and sexual behavior of adolescents, and the social structural factors influencing that behavior. We use existing national data from both Cycles III and IV of the National Survey of Family Growth which were carried out in 1982 and 1988, respectively. Both data sets are quite similar, with the 1988 data being slightly richer in terms of available explanatory variables. Using these 1988 data, we examine the determinants of age at first intercourse, whether contraception was used at this time, and, if not, the time elapsed until first use. We also examine determinants of current use of contraception in 1988. Since we contend that decisions about contraception may be closely linked to decisions concerning sexual activity among teens, we allow for both types of decisions to be jointly determined. Using parallel data from both surveys, we then examine change in the structure of the determinants of age and method choice at first intercourse, of time to first use of contraception, and of current contraceptive method choice. Our estimation procedures are designed to take into account the particular constraints of the data sets and the underlying theoretical problems posed by modelling adolescent sexual and contraceptive behavior.